The proposed research is designed to characterize the action of agents which produce metabolic tolerance on RNA degradation by liver microsomal ribonuclease (RNase). The activity of RNase is determined spectrophotometrically by measuring the appearance of acid-ethanol- soluble nucleotides in an in vitro incubation system containing highly polymerized RNA, buffer and liver microsomal fractions. Studies to be conducted will determine the influence of various tolerance-producing agents on RNA degradation in hepatic and non-hepatic tissue in order to determine the specificity of this effect of inducers on RNase activity.